One type of current sensors as current measuring devices is equipped with a case, a current measuring circuit retained in the case, and a flat long busbar as a shunt resistor; this flat long busbar serves as a ground line extending from a negative terminal (minus terminal) of a storage battery; the case is disposed on the middle portion of the flat busbar. The current measuring circuit measures an electric current being charged into or discharged from the storage battery through the negative terminal of the storage battery and the ground line based on voltage drop across the busbar by the electric current. One example of this type of current sensors is disclosed in Japanese Patent Application Publication No. 2008-39571.